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Until few months back I had only one FTTH broadband connection and a single WiFi router serving my home. Now I added a second FTTH broadband connection (from a different ISP) and added a second WiFi router.

The two WiFi routers (router#1 and router#2) are placed about 2 feet away from each other, and both seem to work fine after a power-cycle but their performance seems to degrade over time (in 4-5 hours). Both routers are 2.4GHz, 300mbps basic SOHO routers. I could still make do with this arrangement to an extent, but coverage was bothering me.

So I bought a 3rd router (router#3) which is a AC1200 dual-band router. This new router (#3) is connected over wired LAN to router#1, and it is configured to operate in router-mode (not as an AP, WISP, range-extender mode).

The introduction of this router seems to be making things worse. I can barely ever connect to this new router and invariably always land up in a 'No internet' state. It seems I can connect to it, after my laptop/mobile have been in airline mode for few hours, and all the routers have just been restarted. After a while this stops working, and my laptop/mobile would invariably have fallen back to the older routers.

As for DNS settings here is what I have:

  • On primary router (directly connected to FTTH converter): DNS --> Google public ones (8.8.8.8 / 8.8.4.4)
  • On secondary router (AC1200, new one, pointing to primary router): DNS --> primary router IP, google public one (8.8.8.8)

Here's a graphic describing the current topology/configuration: enter image description here

Edited: Updated diagram to show both FTTH-ISP connections & all 3 WLAN-routers. The problem seems to be compounded somehow by the relationship between the primary router (router#1) directly connected to FTTH converter, and the secondary router (new AC1200 one - router#3) which points to the primary as gateway.

Looking for some potential causes and suggestions on how to troubleshoot the issues with this new router.

One of my suspicions is some sort of MAC-address conflict. This could be because router#1 sees same device (MAC-id) twice once where device connects to it directly and then due to some transient issue, connects to router#3. Since router#3 then connects to router#1 as gateway, router#1 sees the same MAC-id again. Not sure how to confirm this as the issue or fix it.

It is unlikely to be channel conflict as I have tried explicitly setting to different radio channels (each router -- while scanning neighbourhood radio frequency signal strengths), but finally settled on keeping it auto. In auto channel selection, the router's radio module should select the least busy / least conflicting channel.

Edit: Found some interesting explanation here on cascading routers

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    Some of the most important information is missing. Do all the wireless APs have the same SSID? Are they on the same channel? If yes to both, they are interfering with each other. – tater Aug 15 '20 at 8:58
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    you are talking about 3 routers but your diagram only shows 2. Where is the third one? If the FTTHs are connected to two routers you need to show the physical connection and the setup as well (how do the devices use the two different internet connections?). Also why exactly to you need three routers? How are those set up? DNS has nothing to do with the actual routing. Switches are (more or less) plug and play, routers are not you have to know what you are doing. And please add the IP-addresses to your diagram. – Albin Aug 15 '20 at 15:08
  • Added some clarifications and updated the diagram. – bdutta74 Aug 16 '20 at 16:17
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Impossible to answer without more details but

  • The problem with the two old routers it most likely that their access points use the same frequency and channel which causes interference.
  • The problem with the third router sounds like conflict on layer 3 (OSI model) probable an IP address that's got assigned twice.

At this point, if you don't have "advanced" troubleshooting knowledge and tools I would suggest a strategy to simplify your network setup as much as possible (take out devices and features) until you can pinpoint the problem.

Although this is not part of your question, I would not advise using three routers on the same LAN (segment) unless you separate it physically or by VLAN which does not seem the case.

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  • Thanks Albin. I'd like to go with the 2nd potential problem. Please note that I've assigned separate IP-address ranges to the internal LAN/WLAN for each router (/24 subnet), and so IP-address conflict is very unlikely. What is however likely is some MAC address conflict, and some sort of ARP cache poisoning. – bdutta74 Aug 16 '20 at 16:19
  • @bdutta74 MAC addresses are unique (unless you change/spoof them) a problem will be very unlikely. What makes you think there will be such a conflict? There is still a lot of info missing (IP addresses/leases of the devices, where are the DHCP servers, how do you router between the 3 subnets (if you do that at all) etc.) Did you try to simplify the configuration yet? – Albin Aug 16 '20 at 21:26
  • Also from your diagram, it seems the laptops are connected to two APs at the same time? How do you achieve that? Two wireless network cards in each laptop? – Albin Aug 16 '20 at 21:28
  • Laptops auto-connect to only one router at a time, s.t. if Windows detects 'No internet' high level error with one router, it tries with the other. The diagram is showing only the relationships. Each of the router has it's own DHCP server, dishing out IPs from it's dedicated subnet. Default lease period of 24hrs is set. I do not route between all the 3 subsets. A device can be either connected to router #1, in which case routing happens device -> router#1 -> ISP1. Or, device can be connected to router#, in which case routing is device -> router#2 -> ISP2. ... contd. – bdutta74 Aug 17 '20 at 9:55
  • In case of router#3, routing is device -> router#3 -> router#1 -> ISP1. – bdutta74 Aug 17 '20 at 9:55

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